Island Arc最新文献

Owing to high resistance to alteration, detrital zircons retain information about their formation ages and parental magmas for a long period of time. Many geochemical researchers have proposed various indicators for zircon to constrain tectonic settings and to identify source rock. Because most detrital zircons analyzed by geochronologic studies are derived primarily from granitoids, we focus on the classification of zircon within granitoids. In the style of alphabetical classification scheme (Igneous, I; Sedimentary, S; and Alkaline, A types), some discrimination diagrams have been proposed. To improve the database and enhance discriminating studies, we examined trace-element compositions of zircons extracted from some Cenozoic granitoids exposed in the Japan Islands. The zircons showed systematic differences in Nb, Ta, Ce, and P contents. Zircons in Oceanic Arc I-type granite are poor in Nb and Ta, and these signatures clearly reflect those elements in their parental bodies. Despite their low abundance at the whole-rock level, zircons in Oceanic Arc I-type granite are characterized by high Ce content. This is attributable to the relatively oxidizing conditions of Oceanic Arc I-type magma. Zircons in S-type granite are characterized by high P and low Ce contents. The former can be explained by high apatite solubility in Al-rich magma, whereas the reducing environment of S-type magma is accountable for the latter. The zircon crystallized at the later stage during S-type granite solidification is slightly depleted in Nb and Ta. This is attributable to the depletion of these elements in the magma by Ti-bearing minerals such as ilmenite prior to zircon crystallization. In analogy with whole-rock composition, zircons in transitional I-A-type granite have intermediate composition between I-type and A-type zircons. On the basis of the updated database, we demonstrated that the Nb/P–Ce/P or Ta/P–Ce/P crossplots are the most useful for discriminating zircons in Oceanic Arc I-type, I-type, S-type, and A-type granites.

Stern, R. J. 2024. “Bringing the Submarine Mariana Arc and Backarc Basin to Life for Undergraduates and the Public.” Island Arc 33, no. 1: e12533. https://doi.org/10.1111/iar.12533.

Figures 3 and 4 captions should have been switched as shown below.

FIGURE 3(A) Front of a typical remotely operated vehicle (ROV). Note locations of key features: Lights, cameras (both still and video), manipulator arms, and sample baskets. Modified from NOAA ROV factsheet https://oceanexplorer.noaa.gov/edu/materials/rov-fact-sheet.pdf. (B) A typical ROV control room, from https://schmidtocean.org/cruise-log-post/technology-at-the-seafloor/.

FIGURE 4Schematic section through the upper 140 km of the Mariana convergent margen and subduction zone, showing the principal crustal and upper mantle components and their interactions. Note that the location of the “mantle wedge” (unlabeled) is that part of the mantle beneath the overriding plate and between the trench and the most distal part of the arc where subduction-related igneous or fluid activity is found. Modified after Stern (2002). MF, magmatic front.

We apologize for this error.

The carbonate clumped-isotope thermometer, a relatively recent innovation, is based on the strong relationship between ¹³C-¹⁸O bond abundance in carbonates and their formation temperature. It can measure temperatures solely based on the CO₂ extracted from carbonates and has attracted attention as it accurately reconstructs surface water temperatures on a geological timescale. However, at the time of development, there were many limitations in its application to paleoenvironmental reconstruction such as the large sample size (10 mg), the complicated organic contaminant removal process, and the lack of internationally recognized carbonate standards, and improvements in the measurement method were required. Here, we review the studies conducted since the thermometer development to improve the accuracy and precision of carbonate clumped-isotope analysis. Finally, we discuss advanced carbonate clumped-isotope analysis methods, including laser spectroscopy.

The Baguio District, located in northern Luzon (the Philippines), is one of the major gold and copper mining districts in the Philippines and SE Asia. U–Pb zircon ages for igneous rocks and for detrital zircons extracted from sediment samples of the principal formations of the Baguio District reveal major magmatic pulses at ca. 1, 3, 16, and 20 Ma. The oldest zircon dated in this study has an age of 27.3 ± 1.6 (2σ) indicating earlier activity which has, however, left only a small imprint on the zircon inventory of the sediments. The absence of older zircons suggests that northern Luzon formed as an intra-oceanic arc. Zircon Hf isotope data suggests that the magmas, from which the zircons crystallized, were derived from time-integrated highly depleted mantle sources, compatible with an intra-oceanic origin of the island. The results of the U–Pb dating of zircons mostly confirm previous estimates of the ages of the rock units. Mid-Miocene ages obtained for samples thought to represent the Pugo Formation, the lowermost unit, which is thought to be Cretaceous-Eocene in age, most likely date magmatic rocks that intruded the Pugo Formation.

The granitic intrusions emplaced into a terrane causes several textural, chemical and compositional changes in the host rock by wall-rock alteration and forms contact metamorphic rocks that is, hornfels. The low-grade metasedimentary rocks of the Champaner Group exposed as horse-shoe-shaped map pattern have envisaged several pulses of granitic intrusion with granitoid ages ranging from 2.5 to 0.95–0.93 Ga enclosing its most peripheries. However, it has been observed that the contact metamorphic signatures are most prominent on the eastern periphery of Champaner fading away towards the west slicing up the Champaner Group into outer, middle, and inner zone rocks. The present work is focused on the detailed study of inner zone pelitic hornfels by providing new constraints on field characteristics, reaction textures, mineral chemical compositional analyses, geochemical signatures, and P–T conditions. Three distinguished varieties of pelitic hornfels that is, biotite hornfels, andalusite-cordierite hornfels, and andalusite-sillimanite hornfels with increasing proximity to granitic intrusion respectively were identified. Based on the mesoscopic features, textural and phase relations, and mineral compositions, biotite, andalusite, cordierite, and sillimanite isograds were demarcated. The development of distinct mineral assemblages in different pelitic hornfels is correlated to the varying Al₂O₃, FeO, and MgO content in the bulk rock composition of the rocks and the geometry of the intruding felsic pluton (Godhra granite) beneath the Champaner supracrustals. The geochemical constraints suggest K-rich clay dominant shale protolith of post archean age comparable to Post-Archean Australian Shales (PAAS) deposited in an active continental margin tectonic setting. The increase in temperature gradient rather than pressure induced by 0.95–0.93 Ga “Godhra granitic” intrusion is considered to be a significant factor controlling the development of the observed progressive mineral assemblages. The P–T conditions constrained through P–T pseudosections built in a KFMASHTi model system suggest LP/HT metamorphism with P–T range from 200 to 350 MPa and 530°C–600°C respectively.

The investigation of whole-rock major and trace element geochemical data from metapelites, incorporating analyses from both previous studies and new localities within the Highland Complex (HC) of Sri Lanka and the Trivandrum Block of India (TB), aimed to discern the nature and tectonic setting of their provenance. Examination of chondritic REE distribution and K versus K/Rb diagrams suggests that the geochemistry of the studied metapelites closely resembles typical Post Archaean Australian Shale (PAAS), North American Shale Composite (NASC), and Upper Continental Crust (UCC), indicating minimal modification during high-grade metamorphism. Predominantly, the protoliths of the metasediments appear to be shales and greywackes derived from Proterozoic felsic to intermediate sources. Tectonic discrimination diagrams reveal that most metapelites correspond to active continental margins and continental island arcs. These geochemical characteristics suggest that the majority of studied metapelites in the HC and TB originate from felsic to intermediate sources, likely deposited within a continental arc setting. Subsequently, these sediments likely accreted in an accretionary prism and underwent metamorphism during continental-continental collision. The congruence in geochemical signatures between metapelites in the HC and TB, along with established tectonic, geochronological, petrological, mineralogical, and geophysical correlations, implies that precursor sediments of metasedimentary rocks were likely deposited within a laterally extensive Neoproterozoic sedimentary basin.